Bird flu outbreaks among dairy cows in several states, and at least one infection in a farmer in Texas, have fueled fears that the virus may be the next infectious threat to humans.
The influenza virus, called H5N1, is highly pathogenic, meaning it has the ability to cause severe illness and death. But while its spread among cows was unexpected, people can only catch the virus from close contact with infected animals, not from each other, federal officials said.
“It’s really about people being in environments where they might be interacting with cattle infected with this virus,” said Dr. Dimitris Daskalakis, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention.
“The risk to most others is very low,” he added. “Right now, our risk assessment hasn’t changed, but if it does, we’ll be pretty quick and pretty transparent about it.”
Bird flu is often fatal in birds, but none of the infected cows have died so far. The only symptom in the Texas patient was conjunctivitis, or pink eye, which has also been reported in people infected during other bird flu outbreaks.
The CDC and other agencies in the United States and elsewhere have been tracking H5N1 for years to track its evolution. Federal agencies have stockpiled vaccines and drugs to be used in the event of an outbreak of bird flu.
“We’re more prepared for a flu pandemic than probably any other outbreak that could happen, any other pathogen,” said Rick Bright, chief executive of Bright Global Health, a consulting firm that focuses on improving emergency responses for public health.
Dr. Bright led influenza preparedness at the Biomedical Advanced Research and Development Authority, or BARDA, the federal agency that supports vaccine and emergency drug research, for several years before serving as the agency’s director from 2016 to 2020.
Here’s what you need to know about the H5N1 virus:
Is a human pandemic inevitable?
Among birds and animals, H5N1 avian influenza is already pandemic or panzootic, with infections seen on every continent except Australia. To date, the virus has not evolved into a form that can be easily transmitted from one person to another, and may never do so.
As its name suggests, H5N1 was primarily a problem in birds. But now it has spread to a wide range of species, from seabirds and small scavengers like foxes to large mammals like bears and cows.
There have been sporadic human infections since 1997, when a cluster of cases appeared in Hong Kong. But most patients around the world have come into very close contact with infected animals and generally do not spread the virus to other people.
To become adept at human-to-human transmission, H5N1 would have to pick up several additional mutations and change its shape. The strain isolated from the infected farmer in Texas carries one of these mutations, but this change has occurred before — in humans, foxes and seals, among others — without further consequences.
Human infections so far “fortunately remain a single transmission between species,” said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases who has studied the mutations needed for H5N1 to adapt to humans.
History suggests that even if the virus changes enough to start widespread transmission between humans, it may have to give something up in return, Dr. Munster said. For example, when other flu viruses have adapted to humans, they have lost much of their virulence, causing only mild symptoms.
How will we know if the virus is transmitted to humans?
H5N1 is an influenza virus followed by extensive scientific networks that monitor influenza viruses worldwide.
“We’ve got our eye on it, and we’ve been paying attention to it for years,” said Dr. Daskalakis.
These surveillance networks detected H5N1 even before its outbreak in birds and animals over the past two years. They are now on alert. Scientists are watching for mutations that could make H5N1 more likely to infect humans or be resistant to vaccines and drugs available to fight it.
The World Health Organization, CDC and other global health organizations regularly share information and genetic sequences to track which flu strains are spreading and where.
In the current outbreak, the Department of Agriculture shared genetic sequences from infected cows with the CDC, which analyzes the sequences and ensures that stockpiled vaccines and drugs are still effective.
Do we have a vaccine for bird flu?
Yes.
BARDA has enough building blocks for vaccines — including adjuvants, substances that can boost a vaccine’s strength — to produce millions of doses in weeks. Mass production could also be ramped up quickly if needed, federal officials said.
The CDC already has two candidate viruses that can be used to make vaccines. As the virus changes — acquiring mutations that make it resistant to current vaccines and drugs, for example — federal researchers may create newer candidates.
Three pharmaceutical companies may be asked to make bird flu vaccines, but those vaccines will be made on the same production lines used to make seasonal flu vaccines. Before starting large-scale production, federal officials should consider the consequences of stopping seasonal production, said David Boucher, director of infectious disease preparedness and response at the Department of Health and Human Services.
Not all drug companies use egg-based methods to produce vaccines, which is important because of the potential for bird flu outbreaks to derail the nation’s egg supply. BARDA is also looking to add mRNA to the list of technologies that can be used to make avian flu vaccines. (Covid-19 vaccines made by Pfizer and Moderna were based on the method.)
What about treatments?
At least four antiviral drugs are available to treat people who may become ill with bird flu, including the widely available generic drug oseltamivir, sometimes marketed as Tamiflu.
Unlike vaccines, which are stockpiled by the federal government, antiviral drugs are commercially available. Generic versions of oseltamivir are produced by many manufacturers around the world.
The federal government has a stockpile of tens of millions of doses of oseltamivir, Dr. Bowser said. The government is in close contact with manufacturers who could quickly ramp up production of oseltamivir, as it has done in the past during some bad flu seasons.
All of these preparations are in place for the worst-case scenario, but “we’re not there yet,” said Dr. Bowser. “Our job here is to prepare for the worst and prepare for it should it come.”
